Use of low fluorescence background (LFB) substrates for Raman Spectroscopy investigations is crucial for the generation of high-resolution Raman spectra. Equally significant is the fact that the LFB substrates should exhibit an advanced hydrophobic character that eliminates the spread of the deposited analyte-spots and renders as a result small (concentrated) analyte surface areas. LFB is also a concern for biosensor and large surface area bio-array applications where the desired molecular recognition sites, the ordered spots of the network, should not “communicate” and should retain their individual reactive specificities.
Hydrophobic, low-friction substrates are also crucial for certain applications. For example, catheter guiding wires have to exhibit inert surface characteristics and should have a low surface energy in order to avoid the development of friction forces between the inner surfaces of the catheters and the surfaces of the metal guiding wire during the insertion of the catheter in a living tissue environment, positioning of stents, etc. Current guiding wire surfaces often exhibit rough and non-lubricious surface characteristics. Coating wire surfaces with an inert, highly fluorinated (Teflon-like) thin layer could significantly enhance all operations and safety issues related to the insertion of bioactive devices into “in vivo” environments.
It is known that LFB and very hydrophobic substrates can be produced by the deposition of Teflon or Teflon-like layers using conventional, immersion, spin-coating and spraying technologies. However, Teflon is not soluble in any solvents and modified poly-tetrafluoroethylene macromolecular chains are shy on certain desirable Teflon characteristics, including thermal stability and hydrophobic character. Adhesion of Teflon particles suspended in organic and inorganic media and Teflon-like materials dissolved in organic solvents is often not satisfactory due to the inert nature of the perfluorinated macromolecular chains that create poor adhesion characteristics of the deposited layers.
An alternative approach for the deposition of highly fluorinated organic macromolecular thin layers onto inorganic and organic substrate surfaces is offered by cold-plasma reaction mechanisms. By starting from various fluorinated olefin and paraffin volatile derivatives Teflon-like thin layers may be deposited onto various substrates using plasma deposition techniques. However, the presence of plasma-generated, omnipresent, free radical sites located on the plasma-coated surfaces and generated as a result of the interaction of plasma species with the “nascent” macromolecular thin-layers induce, under open laboratory conditions, oxidation reactions with the formation of polar functionalities. These oxygen containing groups increase the surface energy of the deposited layers and generate reactive surfaces, which significantly reduce the efficiency of the molecular recognition process.